1. Field of the Invention
The present invention pertains to a detecting device that detects information regarding the distance to a target object, e.g., a focus detecting device or distance detecting device employed in a camera.
2. Description of the Related Art
FIG. 7 is a perspective view showing the basic construction of a conventional AF sensor module (focus detecting device) using the phase difference detection method.
The AF sensor module is equipped with condenser lens 101, module mirror 102, aperture mask 103, separator lens 104 and CCD line sensor 105. Condenser lens 101, if used in a single lens reflex camera for example, converges an object photo image that is formed on a film equivalent surface by a photo-taking lens. Module mirror 102 is a reflecting mirror that leads the light that passes through condenser lens 101 to CCD line sensor 105. Aperture mask 103 limits the field of view of plano-convex lenses 104A and 104B of separator lens 104.
Separator lens 104 comprises a pair of small plano-convex lenses 104A and 104B that are molded as one unit, and separates the object photo image into two photo images so that each of the photo images may be re formed at prescribed forming positions on CCD line sensor 105 (a standard area and a reference area). Aperture mask 103 (not completely shown in the drawing) that adjusts the amount of incident light is attached to separator lens 104 on the surface that the light strikes. The optical axes of plano-convex lenses 104A and 104B are decentered relative to each other so that the separated photo images will be formed at their respective image forming positions, e.g., standard area 105A and reference area 105B of CCD line sensor 105.
CCD line sensor 105 is a sensor that has multiple photoelectric conversion elements arranged in a line, and has image forming positions, i.e., standard area 105A and reference area 105B, that are located on either side of and at a prescribed distance from lengthwise center position O.
Separator lens 104 and CCD line sensor 105 are located such that direction A of the lens surface and direction B of the image pickup surface are perpendicular to optical axis L of the object photo image that is led via module mirror 102.
The object photo image led by module mirror 102 is separated into two photo images by means of plano-convex lenses 104A and 104B of separator lens 104. The photo images are then formed on standard area 105A and reference area 105B of CCD line sensor 105 and taken in by standard area 105A and reference area 105B, respectively. Subsequently, based on the difference in image forming position between the image on standard area 105A and the image on reference area 105B (the phase difference), the focus position regarding the photo object is detected by a processor not shown in the drawing.
In addition, a focus detecting device equipped with a filter that eliminates light in the infrared wavelength range has also been proposed (Japanese Laid-Open Patent Application Sho 62-183416), in which the filter surface and the image pickup surface of the image pickup device are arranged such that they are not optically parallel to each other and detection errors due to reflected light existing in the device are reduced.
Because the conventional AF sensor module described above has the lens surface of separator lens 104 and the image pickup surface of CCD line sensor 105 arranged parallel to each other, the light reflected on the image pickup surface of CCD line sensor 105 is reflected again by the convex lens surfaces of separator lens 104 toward CCD line sensor 105, as shown in FIG. 7, for example. Consequently, the reflected light and stray light from said reflection strike the image pickup surface of CCD line sensor 105, and false image signals caused by incident light other than direct light are output.
FIG. 8 is a waveform chart regarding the output signals from CCD line sensor 105 that shows how said signals are output. In this drawing, the positive x-axis side shows the waveform of the output signals from standard area 105A and the negative x-axis side shows the waveform of the output signals from reference area 105B. Signals S1 and S1xe2x80x2 at positions x1 and xe2x88x92x1 are image signals via direct light led via module mirror 102. Signals S2 and S2xe2x80x2 at positions x2 and xe2x88x92x2 are false image signals caused by reflected light existing between separator lens 104 and CCD line sensor 105.
As shown in the drawing, because false image signals S2 and S2xe2x80x2 are output from standard area 105A and reference area 105B, when the phase difference is to be detected by comparing the image on standard area 105A with the image on reference area 105B, said false image signals S2 and S2xe2x80x2 adversely affect the detection and cause an error in the detection result.
On the other hand, in the device disclosed in Japanese Laid-Open Patent Application Sho 62-183416, the infrared light eliminating filter is inclined with regard to the image pickup device so that false image signals caused by light reflected from this filter may be removed. However, in standard AF sensor modules that do not have such an optical filter, it is difficult to effectively eliminate false image signals caused by the light reflected from separator lens 104 as described above.
The present invention was made in view of the problem described above. Its object is to provide a detecting device that reduces detection errors caused by signals generated by received light other than direct light, such as reflected flight and stray light existing in the detecting device, and that is capable of performing highly accurate detection.
Another object of the present invention is to provide, using a simple construction, a detecting device that can prevent light flux other than direct light, such as reflected light and stray light existing in the detecting device, from striking the light-receiving element.
In order to attain said objects, the detecting device of the present invention has an image pickup device including plural photoelectric conversion elements arranged in a line; and an image re-forming lens that re-forms an image of an object formed by a prescribed optical system on an image pickup surface of said image pickup device; wherein a lens surface of said image re-forming lens and said image pickup surface of said image pickup device are arranged such that they are non-parallel to each other.
Using the construction described above, the photo image of the target object that is formed by means of the prescribed optical system is re-formed on the image pickup device. When this happens, even if part of the light flux that pass through the image re-forming lens and strike the image pickup surface of the image pickup device are reflected toward the image re-forming lens and are reflected again by the lens surface of the image re-forming lens toward the image pickup means, the non-parallel arrangement of the lens surface of the image re-forming lens and the image pickup surface of the image pickup device causes the reflected light from the image re-forming lens to veer away from the image pickup surface of the image pickup device. Consequently, said reflected light does not strike the image pickup device again and false image signals caused by the reflected light are not included in the image pickup signals. Therefore, using a simple construction in which the lens surface of the image re-forming lens and the image pickup surface of the image pickup device are arranged to be non-parallel to each other, detection errors caused by stray light, etc. are reduced and the accuracy in detection improves.